Full text of "USPTO Patents Application 10698193"

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Search History 4/26/05 2:04:34 PM Page 2

d2) United States Patent

Ochs et al.

mill

US006317635B1

(10) Patent No.: US 6,317,635 Bl
(45) Date of Patent: Nov. 13, 2001

(54) SENSOR RESPONSIVE ELECTROTHERAPY
APPARATUS

(76) Inventors: Dennis E. Ochs, 2528 170th PL SE.,
Bellevue, WA(US) 98008; Daniel J.
Powers, 2145 Squak Mountain Loop
SW., Issaquah, WA (US) 98027

( * ) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 0 days.

(21) AppL No.: 09/345,590

(22) Filed: Jun. 30, 1999

(51) Int. CI. 7 A61N 1/08

(52) U.S. CI 607/62

(58) Field of Search 607/5-8, 62, 63

(56) References Cited

U.S. PATENT DOCUMENTS
3,747,605 7/1973 Cook.

3,860,009 ♦ 1/1975 Bell et al 128/419

5,115,807 * 5/1992 Pless et al 128/419

5,350,403 * 9/1994 Stroetmann et al 607/5

5,593,427 1/1997 diner et al 607/7

5,601,612 2/1997 Gliner et al 607/7

5,607,454 3/1997 Cameron et al 607/5

5,620,470 4/1997 Gliner et al 607/7

5,836,978 11/1998 Gliner et al. .

FOREIGN PATENT DOCUMENTS

2348139A 9/2000 (GB) .

WO95/09673 4/1995 (WO).

WO97/31680 9/1997 (WO).

W098/47563 10/1998 (WO).

* cited by examiner

Primary Examiner— William E. Kamm
(57) ABSTRACT

An electrotherapy apparatus includes a connecting mecha-
nism coupled between an energy source and a pair of
electrodes for contacting a patient. A controller coupled to
the energy source configures the energy source to provide a
selected one of a plurality of energy levels. The controller
actuates the connecting mechanism to couple the energy
source to the electrodes. A sensor coupled to the controller
measures a parameter or parameters related to the energy
delivered to the patient through the electrodes. The control-
ler performs an operation using the output received from the
sensor. Based upon the operation, the controller actuates the
connecting mechanism to decouple the energy source from
the electrodes. In an embodiment of the electrotherapy
apparatus, the energy source includes a high voltage power
supply for charging a capacitor to a selected one of a
plurality of initial voltages. The sensor includes a voltage
sensor to measure the voltage across the capacitor and a
current sensor to measure the current supplied by the capaci-
tor. The connecting mechanism includes electronic switches
coupled between the capacitor and the electrodes to permit
application of an electrotherapy waveform in either polarity.
The controller performs the operation using the measured
voltages and currents to control the electronic switches. The
operation may include computing the patient impedance,
determining a time constant of the voltage or current,
determining a quantity of charge delivered to the patient, or
determining the time required for the voltage or current to
substantially equal a predetermined fraction of the voltage or
current.

15 Claims, 2 Drawing Sheets

100

102

104

INITIALIZE THE ENERGY SOURCE IN PREPARATION
FOR DELIVERING AN ELECTROTHERAPY WAVEFORM

ACTUATE THE CONNECTING MECHANISM TO COUPLE
THE ENERGY SOURCE TO THE RESISTIVE LOAD
THROUGH THE ELECTRODES

MEASURE A PARAMETER OR PARAMETERS RELATED
TO THE ENERGY DELIVERED TO THE RESISTIVE LOAD

PERFORM AN OPERATION ON THE OUTPUT
OF THE SENSOR FOR DETERMINING CONTROL OF
THE CONNECTING MECHANISM

106

108

ACTUATE THE COUPLING MECHANISM TO DECOUPLE
THE ENERGY SOURCE FROM THE ELECTRODES

4/26/05, EAST Version: 2.0.1.4

U.S. Patent Nov. 13, 2001 Sheet 1 of 2

US 6,317,635 Bl

-30

FIG.1

100

INITIALIZE THE ENERGY SOURCE IN PREPARATION
FOR DELIVERING AN ELECTROTHERAPY WAVEFORM

102

104

106

108

ACTUATE THE CONNECTING MECHANISM TO COUPLE
THE ENERGY SOURCE TO THE RESISTIVE LOAD
THROUGH THE ELECTRODES

MEASURE A PARAMETER OR PARAMETERS RELATED
TO THE ENERGY DELIVERED TO THE RESISTIVE LOAD

PERFORM AN OPERATION ON THE OUTPUT
OF THE SENSOR FOR DETERMINING CONTROL OF
THE CONNECTING MECHANISM

ACTUATE THE COUPLING MECHANISM TO DECOUPLE
THE ENERGY SOURCE FROM THE ELECTRODES

FIG.2

4/26/05, EAST Version: 2.0.1 .4

U.S. Patent Nov. 13, 2001 Sheet 2 of 2

US 6,317,635 Bl

TIME

FIG.3

214

HIGH
VOLTAGE
SUPPLY

"MO- SW1

T30-SW3

SW2

204 0 „ 0 206—,

200 X 202 r

-OT2

210

CURRENT
SENSOR

SW4 -OT4

SW5-OT5

208

VOLTAGE
SENSOR

CONTROLLER

-212

30-

run

T1 T2T3T4T5

FIG.4

4/26/05, EAST Version: 2.0.1.4

US 6,317,635 Bl
1 2

SENSOR RESPONSIVE ELECTROTHERAPY a first parameter related to the energy supplied to the patient

APPARATUS by the capacitor. Additionally, the defibrillator includes a

connecting mechanism coupled between the first terminal

FIELD OF THE INVENTION and the second terminal of capacitor and the first electrode

■ . . . , , _ tl _ , . w 5 and the second electrode. The connecting mechanism per-

This invention relates to the field of electrotherapy More mfts ^ flBt terminal of ^ dlor to seleclivel mu le

particularly, this invention relates to a hardware implemen- t0 one of ^ firs , electrode md ^ electrode and to

tation of an electrotherapy apparatus and a method for using permi , me second termina] of ^ capacitof tQ selectively

the electrotherapy apparatus. couple , Q Qne of , he flrel electrode ^ the sec^d electrode.

BACKGROUND OF THE INVENTION 10 The defibrillator also includes a controller arranged to

receive the first parameter from the sensor. The controller is

Some electrotherapy apparatuses used to perform electro- configured to perform an operation, using the first parameter,

therapy dynamically control the electrotherapy waveform for actuating the connecting mechanism to decouple the

applied to the patient in response to real time impedance capacitor from the first electrode and the second electrode,

measurements made upon the patient. Hardware implemen- 15 The defibrillator also includes a power supply configured for

tations of these electrotherapy apparatuses measure such charging the capacitor to an initial voltage determined by the

parameters as the charge delivered to the patient or the controller,
voltage of the electrotherapy waveform applied to the

patient to estimate the impedance. In response to these DESCRIPTION OF THE DRAWINGS

measurements, the electrotherapy apparatuses adjust the 20 A ^ ^ understandi of the mvention may be

electrotherapy waveform delivered to the patient to improve had from ^ consideration of the followi detailed descri

the effectiveness of the electrotherapy. ^ takeQ {q conjuQCtion ^ thc accompanying drawings

Electrotherapy apparatuses that dynamically control the m which'

elec.rotberapy waveform applied to the patient have imple- nG j shows a ^ ^ b|ock & of an electfo .

mented threshold comparison functions in hardware. Ine ^ theranv annaratus

hardware has included such things as comparators using ^ . . . , , r, r , , r '

voltage references to determine when a measured parameter 2 shows » hl g h level flow d / a S ram 0 I* m f hod f ° r

has reached a threshold value. A cost savings and a reliabil- u f m S ** electrotherapy apparatus shown in FIG. 1 to apply

ity improvement could be realized if the hardware required electrotherapy to a patient.

for implementing the threshold comparison could be sim- 30 FIG. 3 shows an exemplary electrotherapy waveform that

plified. A need exists for an electrotherapy apparatus having could be applied to a patient using the electrotherapy appa-

reduced hardware complexity. ratus shown in FIG. 1.

FIG. 4 shows a simplified schematic of an embodiment of

SUMMARY OF THE INVENTION the electrotherapy apparatus shown in FIG. 1.

Accordingly, an implementation of an electrotherapy 35 DETAILED DESCRIPTION OF THE DRAWINGS
apparatus having reduced hardware and a method lor using

the electrotherapy apparatus have been developed. An elec- The present invention is not limited to the embodiments

trotherapy apparatus for performing electrotherapy on a disclosed in this specification. Although the exemplary

patient through a first electrode and a second electrode 40 embodiments of the electrotherapy apparatus will be ;dis-

includes an energy source to provide energy for performing cussed in the context of an external defibrillator, the prin-

the electrotherapy and a connecting meckanism configured ciples illustrated are applicable to an internal defibrillator,

for coupling and decoupling the energy source, respectively, Additionally, although one of the exemplary embodiments •

to and from the first electrode and the second electrode. The 0 f the electrotherapy apparatus is configured for delivering

electrotherapy apparatus also includes a first sensor config- 45 a bi-phasic electrotherapy waveform, the principles illus-

ured for measuring a first parameter related to the energy trated are applicable to an electrotherapy apparatus which

supplied to the patient by the energy source. Additionally, delivers other electrotherapy waveforms such as a mono-

the electrotherapy apparatus includes a controller arranged phasic electrotherapy waveform, multi-phasic electro-

to receive the first parameter from the first sensor. The therapy waveform, a damped sinusoid electrotherapy

controller is configured to perform an operation, using the 5Q waveform, or the like.

first parameter, for actuating the connecting mechanism to Compensation for impedance variations between patients

decouple the energy source from the first electrode and from mvo lves the measurement of one or more parameters related

the second electrode. to ^ eaergy delivered to the patient. These parameters

An electrotherapy apparatus includes an energy source could include, for example, voltage or current supplied to

and a controller. A method for performing electrotherapy on 55 the patient by the electrotherapy apparatus. The measured

a patient includes coupling the energy source to the patient. parameters, or the results of computations on the measured

The method also includes measuring a first parameter related parameters, are compared to threshold values. Based upon

to energy supplied to the patient. Additionally, the method the result of the comparison, the electrotherapy waveform is

includes performing an operation upon the first parameter adjusted during its application to compensate for impedance

using the controller. The method further includes decoupling 60 variations between patients. Previously, comparison of the

the energy source from the patient based upon the operation. measured values of the parameters to the threshold values

A defibrillator for delivering a multi-phasic waveform to was done using dedicated hardware by using comparators,
a patient through a first electrode and a second electrode Additionally, the threshold values themselves have typically
includes a capacitor having a first terminal and having a been set using dedicated hardware such as voltage refer-
second terminal. The capacitor stores charge used for deliv- 65 ences. The voltage references have been implemented in a
ery of the multi-phasic waveform to the patient. The defibril- variety of ways, such as by using voltage dividers, zener
lator further includes a first sensor configured for measuring diodes, or integrated circuit voltage references.

4/26/05, EAST Version: 2.0.1.4

US 6,317,635 Bl

3 4

A reduction in hardware complexity could be achieved by parameters, related to the energy delivered to the patient,

performing an operation on the parameters using program- Sensor 42 may be, for example, a voltage sensor, a current

mable hardware. By using firmware or software to control sensor, or sensor 42 could be configured to measure both

the hardware with the threshold values specified in the code, voltage and current. Controller 39 uses the values of the

the additional hardware complexity that would be required 5 parameter or parameters provided by sensor 42 to control

to implement the threshold comparison functions is elimi- connecting mechanism 34. The operation performed by

nated. An additional advantage achieved under program controller 38 could include comparing threshold values to

control is the capability to easily configure the electro- the output received from sensor 42. Based upon the result of

therapy apparatus to deliver one of a plurality of energy **** comparison, controller 38 actuates connecting mecha-

levels. Under program control, the operation performed on 10 nism 34 to mntI01 the duration of the electrotherapy wave-

the parameters is adjusted depending upon the selected form applied to resistive load 37. Connecting mechanism 34

energy level and the different threshold values that can be can be actuated to either couple energy source 32 to patient

coded in the software, or firmware, are easily selected. electrodes 36 or decouple energy source 32 from patient

. , c • 1 j electrodes 36 based upon the operation. The operation could

Yet another advantage of an implementaUon under pro- inchide ^ determining the duration of the electro-

gram control is the improved reliability achieved by reduc- is ^ * ^ ^ Qf ^ ^

ingthe hardware .required A hardware implementation usmg Mi ^ iivQl ^ ation performed by controller 38 on

a plurality of threshold values for de ivering one of a ^ values * ^ ^tmztcT or parameters received from

plurality of possible energy levek to the patient would ^ ^ ^ & currcnt mcasurcd

require additional hardware to establish a plurality of refer- sqqsot ^ {Q ^ ^ * delivered t0 lne lient

ence values and a plurality of comparators to perform the 20 determining patient impedance, com-

companson. Alternatively, a switching mechanism could be a ^ m qx dQi ^ { the J e required for

used to selectively connect the plurality of reference values * ^ m qt e tQ substantiall ^ ual a prede \ er mined

to a single comparator This increased complexity decreases e Qr ^ Jq ^

the rehabihty of the electrotherapy apparatus. ^ ^ also £ dude comparing the results of

Shown in FIG. 1 is a high level block diagram of an these computations to threshold values accessed by control-
electrotherapy apparatus 30, such as a defibrillator. The j er 33

electrotherapy apparatus 30 performs electrotherapy on Using controller 38, operating under program control, to

patients and compensates for impedance variations between perform ^ operation the values output from sensor

patients by dynamically controlling the electrotherapy 42 and mreshold values simplifies the hardware needed to

waveform applied to the patients. The implementation of electrotherapy apparatus 30. For example, in

electrotherapy apparatus 30 shown in FIG. 1 is a reduced previous implementations of electrotherapy apparatuses,

hardware implementation. In the electrotherapy apparatus mtegrations were performed in hardware using analog inte-

30, functions previously implemented using dedicated hard- grators ^ resuU of the integration was compared to a

ware are accomplished by the operation performed in con- lhresnold va i ue us i ng dedicated hardware. By using control-

troller 38 under program control, thereby reducing the ^ 38 tQ perform ^ integration and comparison to the

hardware complexity needed for electrotherapy apparatus threshold value under program control, the dedicated hard-

30 ■ ware is ebminated. An additional benefit from performing

Electrotherapy apparatus 30 includes an energy source 32 integration under program control is the ability to achieve a

to provide the energy for the electrotherapy waveform. 40 greater dynamic range in the integration more easily- than

Energy source 32 may include, for example, a single capaci- us j n g dedicated hardware. This allows for dynamic control

tor or a capacitor bank arranged to act as a single capacitor. 0 f the electrotherapy waveform using threshold values (that

A connecting mechanism 34 selectively connects and dis- maVj f or example, be specified in terms of the charge

connects energy source 32 to and from a pair of electrodes delivered to the patient) that can be more simply imple-

36 contacting a patient, with the impedance of the patient 45 mented over a broader range of values with greater accuracy

represented here as a resistive load 37. Connecting mecha- than for a dedicated hardware integrator. Similarly, deter-

nism 34 selectively connects energy source 32 to resistive mining patient impedance, time constants, or the time

load 37 to provide an electrotherapy waveform. Connecting required for voltages or currents to substantially equal

mechanism 34 can selectively connect either side of energy predetermined threshold values, is more easily done over a

source 32 to either one of electrodes 36 to provide an 5Q wide range of energy levels by performing the operation

electrotherapy waveform of either polarity. Controller 38 usmg controller 38 than by using dedicated hardware. :

actuates the connecting mechanism 34 to couple energy In electrotherapy apparatus 30, threshold values for other

source 32 to electrodes 36 or to decouple energy source 32 parameters, such as the maximum allowable current sup-

from electrodes 36. plied Vindicating the possibility of a short circuit) or the

Electrotherapy apparatus 30 could be configured to pro- 55 minimum current supplied by the electrotherapy apparatus

vide a variety of electrotherapy waveforms to a patient, such 30 (indicating a possible open circuit) may be implemented

as a mono -phasic electrotherapy waveform, a truncated in the software or firmware operating controller 38. Per-

exponential bi-phasic waveform, a damped sinusoidal forming these comparisons under program control allows a

waveform, or the like. Energy source 32, connecting mecha- reduction in the hardware needed to perform the over current

nism 34, and controller 38 could be designed to selectively 60 and under current detection functions. Previously, dedicated

permit delivery of any of these types of electrotherapy hardware in addition to that needed for dynamic waveform

waveforms to the patient. Additionally, the electrotherapy control) was used to accomplish the over current and under

waveforms may be delivered by energy source 32 using a current detection.

selected one of a plurality of energy levels set by controller Shown in FIG. 2 is a high level flow diagram of a method

38. 65 for using the hardware shown in FIG. 1 to perform electro -

Controller 38 is coupled to sensor 42 and receives the therapy. First, in step 100, controller 38 initializes energy

output it generates. Sensor 42 measures a*parameter, or source 32 in preparation for delivering an electrotherapy

4/26/05, EAST Version: 2.0.1 .4

US 6,3

waveform to resistive load 37. Next, in step 102, controller
38 actuates connecting mechanism 34 to couple energy
source 32 to resistive load 37 through electrodes 36. Then,
in step 104, sensor 42 measures a parameter, or parameters,
related to the energy delivered to resistive load 37. Next, in
step 106, controller 38 performs an operation on the output
received from sensor 42 for determining control of connect-
ing mechanism 34. The operation may include determining
the charge delivered to the patient, determining a patient
impedance, determining a time constant, or determining the
time required for a current or voltage to substantially equal
a predetermined fraction of the initial voltage or current.
Then, in step 108, controller 38 actuates connecting mecha-
nism 34 to decouple energy source 32 from electrodes 36 to
control the electrotherapy waveform applied to resistive load
37 (representative of the patient impedance) based upon the
parameter. The decoupling is done based upon the operation
to compensate for impedance variations between patients.

Shown in FIG. 3 is an exemplary electrotherapy wave-
form that could be applied to a patient using electrotherapy
apparatus 30. Although the exemplary electrotherapy wave-
form shown in FIG. 3 is a bi-phasic waveform, it should be
recognized that electrotherapy apparatus 30 could be con-
figured to deliver a mono-phasic waveform or an electro-
therapy waveform having more than two phases.

Shown in FIG. 4 is a simplified block diagram showing an
embodiment of electrotherapy apparatus 30 that performs
the operation under firmware control. The embodiment of
electrotherapy apparatus 30 shown in FIG. 4 can be config-
ured for delivering a multi-phasic electrotherapy waveform
to the patient, such as the bi-phasic waveform shown in FIG.
3. Although FIG. 4 shows a specific electrotherapy apparatus
that performs the operation, the disclosed principles are
broadly applicable to electrotherapy apparatuses.

A limitation of a dedicated hardware implementation
using multiple threshold values for delivery of multiple
energy levels to the patient is the complexity of the dedi-
cated hardware required. The implementation of this capa-
bility would require dedicated hardware to set the multiple
threshold values and dedicated hardware to selectively com-
pare the output from the sensors to the threshold values.
However, in the embodiment of the electrotherapy apparatus
30 shown in FIG. 4, these functions are easily implemented
in the firmware that operates controller 212.

The embodiment of the electrotherapy apparatus 30
shown in FIG. 4 includes sensors to measure the voltage and
current supplied by capacitor 200 to patient impedance 202
through first electrode 204 and second electrode 206. Mea-
surement of the voltage supplied by capacitor 200 is per-
formed by voltage sensor 208. Voltage sensor 208 could, for
example, be implemented using a voltage divider network
and a buffer amplifier coupled to the voltage divider. The
voltage divider generates a scaled version of the voltage on
capacitor 200 for the buffer amplifier. The voltage from the
voltage divider is coupled to the buffer amplifier. Measure-
ment of the current supplied by capacitor 200 is performed
by current sensor 210. Current sensor 210 could, for
example, be implemented using a sense resistor coupled in
series with capacitor 200 and an amplifier coupled across the
sense resistor. The sense resistor generates a voltage pro-
portional to the current flowing from capacitor 200. The
voltage output from the amplifier is a scaled version of the
voltage across the sense resistor. Voltage sensor 208 and
current sensor 210 are each coupled to controller 212.
Controller 212 measures the output from each of these
sensors. Controller 212 can use the values of the parameters
measured by voltage sensor 208 and current sensor 210 to

,635 Bl

dynamically control the electrotherapy waveform supplied
to the patient. Dynamic control could be based upon the
current supplied to the patient, the charge supplied to the
patient, the voltage supplied to the patient, or a combination
5 of these.

Controller 212 performs the operation on the values of the
parameters received from one or both of voltage sensor 208
and current sensor 210. Based upon the operation, switches
SW1, SW2, SW3, SW4, and SW5 are closed and opened to

1Q deliver a multi-phasic electrotherapy waveform to patient
impedance 202 through first electrode 204 and second
electrode 206. The duration of each of the phases of the
multi-phasic waveform are determined by the operation
, performed by controller 212 on the values of the parameters
received from one or both of voltage sensor 208 and current

15 sensor 210. By controlling the duration of the phases; the
embodiment of the electrotherapy apparatus 30 can deliver
differently shaped electrotherapy waveforms to the patient.
The operation performed by controller 212 that determines
the durations of each of the phases could be accomplished by

20 computations using the values of the measured parameters.
Alternatively, the operation performed by controller 212; that
determines the durations of each of the phases could be
accomplished with values in a lookup table accessed by
controller 212 using the values of the measured parameters.

25 The operation performed by controller 212 on the values
of the parameters measured by voltage sensor 208 and
current sensor 210 depends upon the method chosen to
implement the dynamic electrotherapy waveform control.
For example, controller 212 could measure either the volt-

30 age or current supplied over a period of time after the
application of the electrotherapy waveform to compute a
time constant. The time constant is dependent upon the value
of capacitor 200 and the resistance in series with ;this
capacitance. The series resistance includes the patient

35 impedance and the resistance in the discharge path of the
capacitor. Control of the electrotherapy waveform based
upon the time constant value would involve sampling either
the voltage or current supplied by capacitor 200, computing
the time constant of the electrotherapy waveform from these

40 values, and then dynamically controlling the waveform
using the computed time constant value. One way to deter-
mine the time constant value would involve computing the
slope of the logarithm of the voltage versus time curve for
the electrotherapy waveform applied to the patient. Using

45 the time constant value, the durations of the phases of the
electrotherapy waveform would be selected from a lookup
table or computed by controller 212. For a bi-phasic elec-
trotherapy waveform, the information in the lookup table
would have first phase durations corresponding to ranges of

50 time constant values. The duration of the second phase could
also be specified in the lookup table or computed based upon
the duration of the first phase.

Alternatively, the operation performed by controller 212
could dynamically control the electrotherapy waveform

55 applied to the patient based upon a time interval required for
the voltage or current supplied to the patient to substantially
equal a predetermined fraction of a value of voltage or
current measured during application of the electrotherapy
waveform. This value of voltage or current could be the peak

60 value of the voltage or current measured near the beginning
of the electrotherapy waveform. Or, this value of voltage or
current could be measured at other times during the appli-
cation of the electrotherapy waveform. For example, this
value of voltage or current could be measured after the

65 instant at which the peak current or voltage occurs.

For dynamic waveform control based upon measurements
by voltage sensor 208, controller 212 could read the voltage

4/26/05, EAST Version: 2.0.1 .4

US 6,317

measured by voltage sensor 208 (the voltage across capaci-
tor 200 which closely approximates the voltage applied to
patient impedance 2021 at the time capacitor 200 is coupled
to patient impedance 202. This corresponds to the peak
value of the voltage supplied to the patient during applica- 5
tion of the electrotherapy waveform. Alternatively, because
controller 212 is used in selecting the initial voltage to which
capacitor 200 is charged, controller 212 could use the value
of the selected initial voltage of capacitor 200 as the peak
voltage supplied by capacitor 200. In another alternative, the 10
voltage on capacitor 200 after the occurrence of the peak
voltage could be measured and used by controller 212 to
perform the operation. The operation performed by control-
ler 212 would include computing a threshold value as a
predetermined fraction of the value of the voltage on capaci- 15
tor 200 (either measured or selected). The time interval
required for the voltage across capacitor 200 to substantially
equal the threshold value changes depending upon the
magnitude of patient impedance 202. The time interval will
be shorter for low impedance patients than it is for high 20
impedance patients. Based upon this time interval, the
operation performed with controller 212 would also include
computing, or selecting from a lookup table, the durations of
the phases of the multi-phasic electrotherapy waveform,
such as the first phase or the second phase of a bi-phasic 2 s
waveform.

Dynamic control of the electrotherapy waveform could
also be accomplished by determining a time interval
required for the current supplied by capacitor 200 to sub-
stantially equal a predetermined fraction of the peak value of 30
the current supplied by capacitor 200. To accomplish this,
the controller 212 would read the measurement of the
current supplied by capacitor 200 made by current sensor
210 to determine the peak current supplied to patient imped-
ance 202. Typically, when electrotherapy is applied, the 35
current supplied to patient impedance 202 will rise from
zero to a peak value shortly after capacitor 200 is coupled to
the patient. The rise time from zero to the peak value is
limited by the inductance in the path through which the
current flows. After reaching the peak value, the current will 40
decay toward zero at a rate determined primarily by the
value of capacitor 200 and the series resistance (which
includes patient impedance 202). The operation performed
by controller 212 would include computing a threshold
value as a predetermined fraction of the peak value of the 45
current. As an alternative to measuring the peak current to
compute a threshold value, controller 212 could read the
measurement of the current supplied by capacitor 200 after
the occurrence of the peak current. The threshold value
would be computed as a predetermined fraction of this 50
measured current.

The time interval required for the current supplied to
patient impedance 202 to substantially equal the threshold
value of the current changes depending upon the magnitude
of patient impedance 202. The time interval will be shorter 55
for low impedance patients than it is for high impedance
patients. The operation performed by the controller 212
would further include determining the time interval required
for the current supplied by capacitor 200 to substantially
equal the threshold value. Based upon this time interval, the
operation performed by controller 212 would also include
computing, or selecting from a lookup table, the durations of
the phases of the multi-phasic electrotherapy waveform,
such as the first phase and the second phase of a bi-phasic
electrotherapy waveform.

In yet another dynamic electrotherapy waveform control
technique, the operation performed by controller 212 would

635 Bl

involve determining the value of patient impedance 202.
Controller 212 would read the voltage and current values
from, respectively, voltage sensor 208 and current sensor
210. The operation performed by controller 212 would
include computing the value of patient impedance 202 based
upon the voltage and current values. Computation of patient
impedance 202 by controller 212 could be done using a
single voltage value and a single current value measured
substantially simultaneously, or, alternatively, a plurality of
pairs of voltage values and current values measured sub-
stantially simultaneously at various times after the start of
the electrotherapy waveform.

The plurality of pairs of voltage values and current values
would be used by the controller to calculate multiple instan-
taneous values of the patient impedance during application
of the electrotherapy waveform. The operation performed by
controller 212 could include averaging these values of
patient impedance. Averaging of the impedance values pro-
vides a more accurate measurement of the patient impedance
than would be obtained from single measurements of volt-
age and current. The measurements and computation of the
patient impedances would be done relatively early in the
application of the electrotherapy waveform so that the
results could be used to adjust the electrotherapy waveform
based upon the calculated patient impedance. Based upon
the computed impedance value, the operation performed by
controller 212 would also include computing, or selecting
from a lookup table, the durations of the phases of the
multi-phasic electrotherapy waveform, such as the first
phase and the second phase of a bi-phasic electrotherapy
waveform.

An additional technique for dynamic control of the elec-
trotherapy waveform determines the duration of the phases
of a multi -phasic electrotherapy waveform depending based
upon the charge delivered to the patient. Controller 212
reads the values of current measured by current sensor 210
after application of the electrotherapy waveform to. the
patient. The operation performed by controller 212 includes
integrating these current values to determine the charge
delivered to the patient over the time in which the measure-
ments were made. The operation performed by controller
212 further includes determining a time interval required for
delivering a predetermined quantity of charge to the patient.
Based upon the time interval, the operation performed by
controller 212 would also include computing, or selecting
from a lookup table, the durations of the phases of: the
multi-phasic electrotherapy waveform, such as the first
phase and the second phase of a bi-phasic electrotherapy
waveform.

An energy source, such as high voltage power supply 214,
is used to charge capacitor 200 to an initial voltage deter-
mined by controller 212. The initial voltage to which capaci-
tor 200 is charged sets the energy level of the electrotherapy
waveform to be applied to patient impedance 202. The initial
voltage is selected by controller 212 from one of a plurality
of possible initial voltages values. Selecting from a plurality
of initial voltages values for charging capacitor 200 is done
in response to operator input. An operator may need to select
the initial voltage because electrotherapy will be applied to
60 the heart, or to a pediatric patient.

Controller 212 dynamically controls the electrotherapy
waveform applied to patient impedance 202 based upon the
parameters supplied by the sensors. Dynamic control of the
electrotherapy waveform permits patients having a wide
65 range of impedances to receive optimal levels of energy.
Depending upon the technique used to perform the dynamic
waveform control, the operation performed by controller

4/26/05, EAST Version: 2.0.1.4

US 6,317,635 Bl

9 10

212 may need to account for the initial voltage to which switches SW1 and SW4 are closed to begin the first phase
capacitor 200 is charged to deliver optimal levels of energy of the bi-phasic electrotherapy waveform. After the begin-
to patients having varying impedances. The threshold values ning of the first phase, voltage sensor 208 measures the
used in the operation performed by controller 212 may voltage across capacitor 200 and current sensor 210 mea-
change depending upon the initial voltage to which capacitor 5 sures the current supplied by capacitor 200. Based upon the
200 is charged. In performing the operation, controller 212 values of either the voltage or the current or the values of
would use a threshold value corresponding to the selected both the voltage and the current, controller 212 performs an
one of the plurality of initial voltage values. For dynamic operation to determine the duration of the first phase and the
electrotherapy waveform control based upon the operation, second phase. At the end of the time interval determined for
the threshold values used by controller 212 would be com- 1Q the first phase, controller 212 opens switch SW5. This
puted or selected from a lookup table dependent upon the interrupts current flow through switches SW1 and SW4and
energy level applied to the patient. For each of the plurality opens these switches, completing the first phase. After :400
of initial voltages to which capacitor 200 could be charged, micro-seconds, controller 212 closes switch SW5 to prepare
there would be a corresponding threshold value used in the for delivering the second phase of the bi-phasic waveform,
operation performed by controller 212. Using a plurality of „ T*™* 50 micro-seconds later, switches SW2 and SW3 are
threshold values is easily done because the different thresh- 15 closed to begin the second phase At the end of the time

old values are selected by the firmware of controller 212. mterval ^^T™ f** 00 ? P hase > c ? ntroll f 21 ?

, ,. . - . , , e A t opens switch SW5. This interrupts current now through

In addition to dynamic electrotherapy waveform control, s ^, ches SW2 and SW3 and £ ^ swUches compl * .

the embodiment of electrotherapy apparatus 30 shown in j n g ^ e ^oo^ phase

FIG. 4 is also well suited to the detection of over-current and 20 Mth h several embodiments 0 f the invention have been

under-current conditions during the application of electro- disc ] osed> various modifications may be made without

therapy. Current sensor 210 measures the current supplied d ^ from ^ of ^ ded daims

by capacitor 200 at the end of the first 100 micro-seconds what is claimed is-

following application of the electrotherapy waveform to j M electrotherapy apparatus for performing electro-
detect the over-current or undercurrent condition. The 25 therapy on a p atient through a first electrode and a second
threshold values that indicate the presence of either an electrode) ^ electrotherapy apparatus comprising:
over-current condition or an under-current condition change K t0 provide ea ergy for performing the
with the energy level used for the electrotherapy. . bJ , r bJ r &

Detection of either an over-current or an under-current & l^J^^chmism configured for coupling ^and

condition results in termination of the electrotherapy wave- 30 , ,. * t . 0rt „„ M tl^T**™

e „_ r . j. . * J* i decoupling the energy source, respectively, to and trom

form. The presence of an under-current condition indicates a r . ? . , °\ j i * a

uv. a a i ♦ a >u ♦ the first electrode and the second electrode;

the possibility of damaged electrodes or electrodes that are _ _ . c _ [ ■

not connected to the patient. The presence of an over-current a first sensor configured for measuring ; a first parameter

condition indicates the possibility of a short circuit. The related t0 energy supplied to the patient by ; the

threshold values for the over-current and the under-current 35 energy source, an

detection can be computed from the initial voltage to which a controller arranged to receive the first parameter from

capacitor 200 is charged. The initial voltage could be the first sensor and configured to perform an operation

obtained by reading the output of voltage sensor 208. , using the first parameter, for actuating the connecting

Alternatively, the threshold values for the over-current and mechanism to decouple the energy source from the first

the under-current detection can be selected from a lookup 40 electrode and the second electrode, wherein:

table based upon the initial voltage to which capacitor 200 tne operation includes determining a time constant based

is charged. The threshold values are computed by controller upon the first parameter.

212 using the upper and lower limits of the expected values 2. The electrotherapy apparatus as recited in claim 1,

of patient impedance 202 (respectively, 180 ohms and 25 wherein:

ohms) and subtracting or adding a small value to provide for 45 the controller includes a configuration to control: the

possible measurement error. The values of the measured energy source to provide a selected one of a plurality of

current road from current sensor 210 are compared by energy levels for the electrotherapy and to perform the

controller 212 to the corresponding threshold values to operation using a value corresponding to the selected

determine whether an over-current or an under-current con- one of the plurality of energy levels for the electro-

dition is present. 50 therapy.

Operation of the embodiment of electrotherapy apparatus 3. The electrotherapy apparatus as recited in claim 2,

30 shown in FIG. 4 will be explained for the case in which wherein:

switch SW5 is an insulated gate bipolar transistor and the controller includes a configuration to actuate; the

switches SW1-SW4 are silicon controlled rectifiers. connecting mechanism to perform a first phase of the

However, it should be recognized that other types of elec- 55 electrotherapy having . a first duration based upon the

tronic or electro-mechanical switches could be used to operation and to actuate the connecting mechanism to

deliver the electrotherapy waveform. For other types of perform a second phase of the electrotherapy having a

switching devices, the order in which switches SW1^SW5 second duration based upon the operation,

are actuated may be different. Additionally, operation of the 4. The electrotherapy apparatus as recited in claim 3,

embodiment of electrotherapy apparatus 30 will be eo wherein:.

explained for the case in which the multi -phasic waveform the first parameter includes either a current or a voltage

applied includes a bi-phasic waveform. supplied by the energy source to the patient.

In preparation for delivering a bi-phasic electrotherapy 5. An electrotherapy apparatus for performing electro-
waveform, controller 212 configures high voltage power therapy on a patient through a first electrode and a second
supply 214 to charge capacitor 200 to a selected initial 65 electrode, the electrotherapy apparatus comprising:
voltage. Then controller 212 closes switch SW5 to prepare an energy source to provide energy for performing the
for delivering the first phase of a bi-phasic waveform. Next, electrotherapy;

4/26/05, EAST Version: 2.0.1.-4

US 6,317,'

a connecting mechanism configured for coupling and
decoupling the energy source, respectively, to and from
the first electrode and the second electrode;

a first sensor configured for measuring a first parameter
related to the energy supplied to the patient by the 5
energy source; and

a controller arranged to receive the first parameter from
the first sensor and configured to perform an operation,
using the first parameter, for actuating the connecting
mechanism to decouple the energy source from the first 10
electrode and the second electrode, wherein:

the operation includes determining a first time interval
beginning with the first sensor measuring a first value
of the first parameter and ending with the first sensor 5
measuring a second value of the first parameter sub-
stantially equal to a predetermined fraction of the first
value; and

the controller includes a configuration to actuate the
connecting mechanism to couple the energy source to 2 o
the first electrode and the second electrode and to
decouple the energy source from the first electrode and
the second electrode at the end of a second time interval
determined by the operation and having a first duration
based upon the first time interval. 2 5

6. The electrotherapy apparatus as recited in claim 5,
wherein:

the controller includes a configuration to actuate the
connecting mechanism to couple the energy source to
the first electrode and the second electrode after the 30
second time interval and to decouple the energy source
from the first electrode and the second electrode at the
end of a third time interval determined by the operation
and having a second duration based upon the first time
interval. 35

7. The electrotherapy apparatus as recited in claim 6,
wherein:

the controller includes a configuration to control the
energy source to provide a selected one of a plurality of
energy levels for the electrotherapy and to perform the 40
operation to determine the second time interval and the
third time interval using a value corresponding to the
selected one of the plurality of energy levels for the
electrotherapy.

8. The electrotherapy apparatus as recited in claim 7, 45
wherein:

the first parameter includes either a current or a voltage
supplied by the energy source to the patient.

9. An electrotherapy apparatus for performing electro-
therapy on a patient through a first electrode and a second 50
electrode, the electrotherapy apparatus comprising:

an energy source to provide energy for performing the
electrotherapy;

a connecting mechanism configured for coupling and 55
decoupling the energy source, respectively, to and from
the first electrode and the second electrode;

a first sensor configured for measuring a first parameter
related to the energy supplied to the patient by the
energy source; and 60

the first parameter includes a current supplied by the
energy source to the patient;

635 Bl

the operation includes determining a charge delivered to
the patient using the first parameter and determining a
first time interval beginning with the coupling of the
energy source to the first electrode and the second
electrode and ending with the charge delivered to the
patient substantially equaling a predetermined value;
and

the controller includes a configuration to actuate the
connecting mechanism to couple the energy source to
the first electrode and the second electrode and to
decouple the energy source from the first electrode and
the second electrode at the end of a second time interval
determined by the operation and having a first duration
based upon the first time interval.

10. The electrotherapy apparatus as recited in claim 9,
wherein:

the controller includes a configuration to actuate: the
connecting mechanism to couple the energy source to
the first electrode and the second electrode after the
second time interval and to decouple the energy source
from the first electrode and the second electrode at the
end of a third time interval determined by the operation
and having a second duration based upon the first time
interval.

11. The electrotherapy apparatus as recited in claim 10,
wherein:

the controller includes a configuration to control the
energy source to provide a selected one of a plurality of
energy levels for the electrotherapy and to perform the
operation to determine the second time interval and the
third time interval using a value corresponding to the
selected one of the plurality of energy levels for the
electrotherapy

12. The electrotherapy apparatus as recited in claim 11,
wherein:

the energy source includes a capacitor coupled to a power
supply; and

the energy source includes a configuration to charge the
capacitor to a selected one of a plurality of voltages
corresponding to the selected one of the plurality of
energy levels.

13. The electrotherapy apparatus as recited in claim 12,
wherein:

the operation includes determining the first, time interval
based upon a time required for the charge delivered to
the patient to substantially equal a selected one of a
plurality of predetermined values, including the prede-
termined value, corresponding to the selected one of
the plurality of voltages.

14. The electrotherapy apparatus as recited in claim 13,
wherein:

the controller includes a configuration to determine a
maximum allowable current and a minimum allowable
current based upon the selected one of the plurality of
voltages and to actuate the connecting mechanism to
decouple the energy source from the first electrode and
the second electrode for a value of the first parameter
greater than the maximum allowable current or .less
than the minimum allowable current.

15. An electrotherapy apparatus for performing electro-
therapy on a patient through a first electrode and a second
electrode, the electrotherapy apparatus comprising:

an energy source to provide energy for performing the
electrotherapy;

a connecting mechanism configured for coupling and
decoupling the energy source, respectively, to and from
the first electrode and the second electrode;

4/26/05, EAST Version: 2.0.1.4

US 6,317,635 Bl

a first sensor configured for measuring a first parameter

related to the energy supplied to the patient by the

energy source;
a memory storing a threshold value and a set of program

instructions; and
a processing unit coupled to the memory and the first

sensor, the processing unit configured to perform a

comparison operation in accordance with the set of
program instructions, using the first parameter and the
threshold value stored in the memory, for actuating the
connecting mechanism to decouple the energy source
from the first electrode and the second electrode. :

4/26/05, EAST Version: 2.0.1.4

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Full text of "USPTO Patents Application 10698193"

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